Isolating a section of already-ballasted track?

[jwb]

The best way to make sure the rails stay straight is to put a Kadee style track gauge on either side of the place where you are going to make the cut. This will help keep the saw action from pulling the rails loose while you cut. Otherwise yes, make the cut and fill the gap with styrene held in place with CA glue. Also, make the cut on a straight section of track.